The present invention relates to a vehicle seat and, more particularly, to a vehicle seat having a mechanism for moving a headrest in a rear-end collision.
When a collision of a vehicle, such as an automobile, occurs from the rear (a so-called rear-end collision), the head of a seated passenger is moved suddenly to the rear by inertia, and the neck may be shocked. Therefore, there has conventionally been known a vehicle seat provided with a configuration for buffering a shock by moving the headrest to the front and supporting the passenger's head at the time of the occurrence of the rear-end collision to protect the head, the neck, and the like of the passenger from the shock in a rear-end collision (see, e.g., Japanese Unexamined Patent Application Publication No. 2006-182094 (“the '094 Application”)).
The vehicle seat described in the '094 Application has a configuration in which a plate body is mounted to a seat back frame of a seat back to be movable back and forth, a headrest is mounted in the upper part of the seat back frame to be movable by an upper link, a lower link connected to the plate body is rotatably provided in the lower part of the seat back frame, and the lower link and the upper link are connected to each other by a transmission member, and is configured so that a load sensed by the plate body at the time of rear-end collision is transmitted from the lower link to the upper link to move the headrest to the front.
For this vehicle seat, the load at the time when the passenger is moved to the rear by rear-end collision is received by a portion near the waist having a rearward displacement larger than that of the back, whereby the rear-end collision can be sensed with certainty. Also, by the configuration in which the load received by the plate body is transmitted to the upper link via the lower link and the transmission member, the load can be transmitted to the upper link with high transmission efficiency, so that the operation for moving the headrest to the front becomes reliable.
The lower link of the vehicle seat is configured as shown in FIG. 6. As shown in FIG. 6, a lower link 91 is rotatably fixed on the inside of a side frame 90 of the seat back frame by a shaft 92. Also, the lower end part of a transmission member 95 is rotatably connected to a portion below the shaft 92 of the lower link 91 via a shaft 93. Further, in a lower part of the lower link 91, a wire spring 98 is locked to a locking hole 94, so that the lower link 91 is connected to the plate body via the wire spring 98.
When the passenger is moved to the rear by a rear-end collision and a rearward load is applied to the plate body, the plate body is moved to the rear, whereby the wire spring 98 is moved to the rear. Then, the lower part of the lower link 91 is pulled to the rear by the wire spring 98, and is rotated to the rear around the shaft 92. When the lower part of the lower link 91 is rotated to the rear, the transmission member 95 connected to the lower link 91 moves to the rear. This rearward movement of the transmission member 95 is transmitted to the upper link, whereby the upper link is rotated to the front. Thereby, the headrest is moved to the front to support the passenger's head. The lower link 91 and the transmission member 95 are configured so that the rotating direction and the movement direction thereof are substantially parallel with the side frame 90.
In the technique described in the '094 Application, since the lower link 91 is attached to the side frame 90 by only one shaft 92, when a shock (load) applied to the plate body by a rear-end collision is transmitted to the lower link 91 via the wire spring 98, and the load is applied suddenly to the inside direction of the side frame 90, the lower link 91 is sometimes rotated to the slantwise direction with respect to the direction parallel with the side frame 90.
If the lower link 91 is rotated in a state of being slantwise tilted with respect to the direction parallel with the side frame 90 while being attached to the side frame 90 by the shaft 92, the transmission member 95 connected to the lower link 91 moves in a state of being tilted to the slantwise direction, that is, to the inside direction or the outside direction of the seat back frame, and further the upper link connected to the transmission member 95 rotates in a state of being slantwise tilted.
If the link mechanism operates in a state of being slantwise tilted with respect to the direction parallel with the side frame 90, that is, the inherent rotating direction, a loss occurs in the load for moving the headrest to the front, which load is transmitted from the plate body to the headrest via the link mechanism. Thus, by the operation of link mechanism in a slantwise tilted state, the load for moving the headrest to the front sometimes cannot be maximally used.